This invention relates to radio frequency power modules and, in particular, to power metal semiconductor field effect transistors (MESFETs).
Power MESFETs are often utilized in portable, cellular radio transmitters. Unfortunately, the useful range of these MESFETs exists only up to the point of reverse breakdown voltage (i.e., in the linear region of the drain current). When the drain voltage increases past the reverse breakdown voltage point, the drain current, and consequently the power, increases rapidly in the transmitter. Thus, the higher the reverse breakdown voltage in the MESFET, the more efficient the transmitter will be since the size of the battery and heat sinks needed in the transmitter can be reduced. The battery size required can be reduced due to decreased current drain and the heat sinks can be reduced in size due to decreased power.
Prior art power MESFETs utilizing a single gate provide an inadequate reverse breakdown voltage for many applications. For instance, when the gate voltage is zero and the drain current is 12 mA, a prior art device having a four cell structure with total gate width of 12 mm. has a reverse breakdown voltage of approximately only 24 V. A new power MESFE providing a higher reverse breakdown voltage is needed to produce smaller and more efficient radio transmitters.